1. Field of the Invention
This invention relates to ball valves and more specifically to an improvement in a ball valve and a process for its manufacture.
2. Description of the Prior Art
Ball valves having a rotary member with a generally spherical shape are well-known. Such a valve is opened by rotation of the rotary ball member, which has a flow passage therethrough, so that it is aligned with the flow passage of the housing in which the rotary member is mounted. Conversely, the valve is closed by rotating the rotary member so that the passage through the rotary ball member is out of alignment with the passage of the housing in which the rotary member is mounted. Normally when the valve is closed, the passage through the rotary member is positioned 90.degree. crosswise with the flow passage of the housing. In any event, when the rotary member is closed, a portion of its solid spherical surface blocks the flow passage through the housing.
The seal between the flow passage of the housing and the flow passage of the rotary member must be sufficiently good that there is no leakage therepast when the rotary member is either closed or open. If flow is expected in either direction, or just to provide back-up leakage security, appropriate seals are located at both passage ends of the rotary member.
Teflon forms a good seal material, although other deformable or yieldable materials have been successfully employed. Seals which are pre-loaded are more satisfactory than those that are not because they are more responsive following a movement of parts and because they generally conform more tightly to the adjacent surfaces, thereby creating a resistance to pressure leaks.
One popular ball valve of the type just described is disclosed in U.S. Pat. No. 3,807,692, Usab, et al., which is incorporated herein by reference for all purposes. The annular seals disclosed in this structure operate in conjunction with recess surfaces located abutting and surrounding the respective ends of the passage through the rotary ball member. When the rotary member is rotated closed, the seals are axially pushed out of their respective recess surfaces and away from the ball member. In order to permit this axial movement of the seals, the inside perimeter of the housing must be larger than the inside perimeter of the seals and the rotary ball member passage.
Moreover, the step passage dimension just described wherein the housing passage is larger than the rotary member passage allows a two-part core or mandrel to be inserted from either side of the passage of the ball member and the seals to provide preloading of the seals with respect to shoulders on the mandrel parts during the injection molding process of making the ball valve assembly. That is, while the seals are thus preloaded, the ball member, seals and mandrel is enclosed within an appropriate injection mold wherein the housing is formed. Once the molding is complete, the mandrel is then removed and the mold taken apart, thereby leaving the ball member and the pre-loaded seals in place.
As mentioned above, the '692 structure provides a structure for creating pre-loaded seals and to allow their operation. However, it does so by creating a two-step passageway through the valve. Such a passageway produces turbulence in the flow of the fluid passing therethrough, even to the degree that produces axial shock waves in the flow, and causes erosion of the parts at the step. Since the seals are located at the step, the seals carry the brunt of this adverse action and, hence, seal failure can result.
Therefore, it is a feature of the present invention to provide an improved ball member structure having pre-loaded seals wherein the ball member passage and housing passage are of equal inside perimeter dimension.
It is another feature of the present invention to provide an improved ball member passage and housing passage of equal dimension with a preloaded seal therebetween.
It is still another feature of the present invention to provide an improved mandrel for preloading seals in a ball valve structure having retractable surfaces, rather than fixed dimensioned shoulders, so as to allow a passage through the valve of uniform inside dimension.